Results
Light microscope (LM) and scanning electron microscope (SEM) measurements
Sizes of pollen grains were calibrated by lengths of equatorial axis and polar axis under light microscopy. The average length of grain samples is 27.31 μm in Polar view (14.4- 51.7μm) and 30.62 μm on polar axis in equatorial view (18.33- 60.7 μm) (Table 3; Figure 2 and 3). Pollen shapes were classified as categories by Erdtman (1952). Under light microscope measurements, the shape of pollen grains ranges from suboblate (P/E = 0.75-0.88), through oblate-spheroidal, prolate-spheroidal, and subprolate, to prolate (P/E = 1.33-2). The range of P/E index of all specimens is from 0.75 to 1.84. There is significant difference in P/E ratios between three Quercus sections and between 22 oak species. Polar area (p/D ) is the ratio of the distance between two furrows and the length of the grain in polar view.p /D of all specimens is from 0.21 to 1.17 (average in 0.64) (Table 3; Figure 4, 5, and 6). I applied T-test on 20 species (excluding hybrid QuercusChrysolepis , andNotholithocarpus ). The results suggest that there are significant different between sizes and shapes of each species, each section, and evergreen-decidous oaks (Table 4). Then, I applied Moran’s tests on 20 species (excluded hybrid species, Chrysolepis chrysophylla , and Notholithocarpus densiflorus ) to test phylogenetic signals. There is only the length of polar view passed Moran’s test (p <0.05; p = 0.041 and 0.042 in 2 tests) when I tested 20 species at the same time (Table 5 and 6).
Most California Quercus pollen have scabrate or verrucate ornamentations on surface. The surface structural patterns of exine displayed under SEM are psilate-verrucate, verrucate, verrucate-scabrate, and psilate-scabrate (Table 7). Structural patterns include perforations of varying density (sparse or dense) and varying distribution (regular or irregular). Most modern Quercus species irregularly perform scabrates on pollen surface.